_bittestandset, _bittestandset64

Microsoft Specific

Generate the bts instruction, which examines bit b of the address a, returns its current value, and sets the bit to 1.

unsigned char _bittestandset(
 long *a,
 long b
);
unsigned char _bittestandset64(
 __int64 *a,
 __int64 b
);

Parameters

• [in, out] a
  A pointer to the memory to examine.

• [in] b
  The bit position to test.

Return Value

The bit at the position specified.

Requirements

Header file <intrin.h>

Remarks

On the IPF architecture, the bts instruction is not available, so this intrinsic is a custom function that imitates the behavior of bts. This custom function might be slower than a hand-written inline function because it includes overhead, such as handling the case where b is negative, that might be unnecessary in specific cases.

This routine is only available as an intrinsic.

Example

// bittestandset.cpp
// processor: x86, IPF, x64
// This example uses several of the _bittest family of intrinsics
// to implement a Flags class that allows bit level access to an
// integer field.
#include <stdio.h>
#include <intrin.h>
#pragma intrinsic(_bittestandset, _bittestandreset,\
 _bittestandcomplement, _bittest)
class Flags
{
private:
 long flags;
 long* oldValues;
public:
 Flags() : flags(0)
 {
 oldValues = new long[32];
 }
 ~Flags()
 {
 delete oldValues;
 }
 void SetFlagBit(long nBit)
 {
 // We omit range checks on the argument
 oldValues[nBit] = _bittestandset(&flags, nBit);
 printf_s("Flags: 0x%x\n", flags);
 }
 void ClearFlagBit(long nBit)
 {
 oldValues[nBit] = _bittestandreset(&flags, nBit);
 printf_s("Flags: 0x%x\n", flags);
 }
 unsigned char GetFlagBit(long nBit)
 {
 unsigned char result = _bittest(&flags, nBit);
 printf_s("Flags: 0x%x\n", flags);
 return result;
 }
 void RestoreFlagBit(long nBit)
 {
 if (oldValues[nBit])
 oldValues[nBit] = _bittestandset(&flags, nBit);
 else
 oldValues[nBit] = _bittestandreset(&flags, nBit);
 printf_s("Flags: 0x%x\n", flags); 
 }
 unsigned char ToggleBit(long nBit)
 {
 unsigned char result = _bittestandcomplement(&flags, nBit);
 printf_s("Flags: 0x%x\n", flags);
 return result;
 }
};
int main()
{
 Flags f;
 f.SetFlagBit(1);
 f.SetFlagBit(2);
 f.SetFlagBit(3);
 f.ClearFlagBit(3);
 f.ToggleBit(1);
 f.RestoreFlagBit(2);
}

Flags: 0x2
Flags: 0x6
Flags: 0xe
Flags: 0x6
Flags: 0x4
Flags: 0x0

See Also

Reference

Compiler Intrinsics